In the medical treatment of certain conditions of the eye, it is sometimes necessary or desirable to form a groove in the cornea. The groove may be formed near the outer perimeter of the cornea so that replacement corneal tissue can be tucked into the groove and sewed in place.
The groove, which may be annular, can be formed by making two intersecting cuts in the cornea. These cuts must be made very carefully to a shallow depth which may be, for example, about 0.2 to about 0.4 millimeters (mm). It is extremely difficult to carefully and accurately make shallow incisions on the corneal surface due to the non-rigid nature of the eye.
A trephine can be used to make an incision in the cornea. One prior art trephine includes a hollow cylinder having a cylindrical razor blade at one end for forming a generally vertical cut in the periphery of the cornea for 360 degrees. Scissors are then used to manually form an angle cut in the cornea which intersects the vertical cut, and the resulting segment can be removed from the cornea to provide a groove. Unfortunately, it is exceedingly difficult to accurately control the scissors-cutting operation, and it takes a relatively long time to complete the scissors cut.
Lieberman U.S. Pat. No. 4,423,728 discloses a trephine which can make both of the cuts in the cornea, thereby eliminating the need for a scissors cut. However, this trephine is very complex and provides for numerous adjustments of the blade which introduce a possibility of human error in the corneal-cutting procedure.